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Entries in whale sharks (38)

Tuesday
Jul062010

Whale shark news roundup

Photo: Bruce Carlson/Marj Awai

There’s a heck of a lot going on in the world of whale sharks right now, so I thought a news roundup was in order.

Blogger GrrlScientist has a nice blog post up about whale sharks right now, over at Scientist Interrupted

Sad news about a whale shark that was trapped in fishing nets in Pakistan and died. I have no idea what the scientist is talking about when he describes them as “inefficient swimmers”; as far as we know they are paragons of efficiency. I also have my suspicions about whether this animal was actually dead when it was brought back to shore. In a different story about the same event, it described the animal as being alive when the fisherman found it, tail-looped it and dragged it back to the beach, and how its illegal to fish for them, but legal to use them as you like if they die accidentally, hmmm....  Without witnesses, I guess we'll never know.

Our collaborator Bob Hueter from the Shark Research Lab at Mote Marine Laboratory is following an animal dubbed Sara in the Gulf of Mexico, who has been affixed with a real-time satellite tag. So far she is avoiding the worst affected area of the BP oil spill, which is a relief. Follow her movements here.

Unfortunately, other whale sharks don’t appear to be avoiding the pollution. NOAA scientists last week observed whale sharks among ribbons of surface oil, not 4 miles from the Deepwater Horizon wellhead. If whale sharks are unable to avoid the oil, it’s a potential disaster because the anatomy of their gills and filter-feeding apparatus are superbly susceptible to fouling, as I discussed in a recent blog post.

One of my projects is getting a bit of press this week. Georgia Aquarium has entered into a collaboration with the Core Sequencing Facility at Emory University to start sequencing the genome of the whale shark. It’s a huge job, but the lab at Emory, led by Dr. Tim Read, are up to the task! They’re using Roche 454 pyrosequencers to generate a survey sequence right now, from DNA we isolated in the lab at the aquarium. Its exciting stuff and was picked up on the AP wire. Read an example here, or just google “whale shark genome emory”

University of Southern Mississippi research Eric Hoffmayer was lucky enough to observe an aggregation of about 100 whale sharks off the coast of Louisiana last week, accompanied by legendary marine explorer and Nat Geo guru Sylvia Earle.  Eric has been working with that population for some time, but as far as I know thats the most he's ever seen in one place.  Lets hope they are animals avoiding the oil spill.


And, finally, the 3rd annual Whale Shark Festival is scheduled to get underway in Isla Mujeres, Mexico, next Friday the 16th.  I'll be there with other scientists including Bob Hueter and Rafael de la Parra, talking publically about whale sharks in the Gulf and the other amazing marine biology of the Yucatan.  There's also going to be a film festival and cultural activities highlighting Quintana Roo.  Did you know that "shark" is one of the only English words with a Yucatec Indian origin?  Its comes from the Mayan "Xoc".  Hope you can join us!

Friday
Jul022010

Implications of the first sighting of whale sharks in the gulf oil slick

I recently experienced a moment of genuine dread regarding the oil spill in the Gulf of Mexico, and it was neither a familiar nor comfortable feeling. What is it that invoked such a powerful feeling after a disaster that has been underway for the last 80-odd days, now? Something that struck a little close to home, of course: the first direct impact to whale sharks. You may have seen this story coming across the wires over the past two days about NOAA scientists who, while on an aerial survey of the impacted area, observed 3 whale sharks swimming among ribbons of surface oil, not 4 miles from the epicenter of the Deepwater Horizon spill. This observation has serious implications; let me explain.

Whale sharks are widely-ranging tropical migratory sharks that are unusual among their more toothy relatives in that they eat plankton. Two of the adaptations they use to pursue this lifestyle – surface filter feeding and an exquisite sense of smell – make them especially susceptible to the impacts of the oil spill. I had all but convinced myself (perhaps wishfully thinking) that whale sharks would be able to sense the altered chemistry of the affected water bodies and avoid the area. It now seems that this is not the case; the observation by the NOAA scientists suggest that either whale sharks cannot tell the difference between polluted and unpolluted water, or they can tell the difference but do not alter their behaviour in such a way as to avoid the ribbons and plumes. As USM researcher Eric Hoffmayer states in the article, this is the realization of the worst fears of whale shark scientists, and I count myself among those.

How can it be that whale sharks are unable to tell the difference if their sense of smell is so good? One simple explanation is that the olfactory abilities may be extremely selective. Scientists don’t know exactly what sort of chemicals whale sharks are homing in on when they seek out patches of food in the ocean – indeed, addressing this question is one of the goals of this year’s whale shark research program at Georgia Aquarium – but we have some good candidate molecules. If the whale shark sense of smell is highly tuned to these compounds and relatively insensitive to other families of chemicals, like hydrocarbons (oil and gas), then it’s certainly possible that whale sharks simply cannot detect the problem.

That’s when the second adaptation, surface filter feeding, becomes a liability for whale sharks trying to negotiate the deadly emulsions and surface slicks in the Gulf. To fully appreciate why this is such a problem, we need to look a little more closely at the filtration apparatus whale sharks use to feed.

Like most plankton-feeding fishes, whale sharks use filters in the mouth/gill cavity to sift food particles from the water (see the exellent illustration by Emily Damstra at right). And like most plankton-feeding fishes, these filters develop from structures associated with the gills and gill rakers (cartilaginous rods that come off the leading edge of the gills and protect the gills from fouling and shape the current of water across the breathing surface). Where whale sharks differ radically from other planktivores like, say, anchovies, is that they do not have feathery interlocking gill rakers that serve to filter the plankton but can be disengaged from each other to allow bulk water flow out through the gill opening. Rather, their filters are so derived and so heavily branched that they form a single continuous pad that occupies the space between gill arches; it looks a lot like a black scouring pad. The gill arches cannot be disengaged from each other; thus, anything that goes in the mouth must be small enough to pass through the filters (less than 2mm, or about 1/12th of an inch), or it must be swallowed, or be spat back out through the mouth (something they are surprisingly good at!). In a paper currently in the review process, comparative anatomist Phil Motta from USF is describing the full functional anatomy of these structures; he took the photo of the filter pad surface shown hereabouts based on material samples from Georgia Aquarium.

The implication here is that oil that finds its way into the mouth, if it is not to be swallowed or to foul the filters, must be continually spat back. OK, I hear you say, perhaps if the whale sharks avoid feeding, there won’t be a problem. If only it were that easy. Whale sharks do not only use their mouths for feeding, they use them for breathing. They need to be passing water continually across the filters and thence across the gills, in order to keep the body supplied with oxygen. For the whale shark swimming in oil-affected waters, therefore, the animal’s breathing needs and the susceptibility of their feeding filters to fouling are in complete opposition.

If whale sharks are swimming into oil-polluted waters and fouling their filters with oil, what does that mean? In my best estimation, it means that the oil spill represents an extremely serious threat to whale shark health. I am by no means the first person to suggest this. Nature identified whale sharks as one of the 5 species most likely to be affected by the oil spill, and other scientists like Bob Hueter from Mote Marine Laboratory have also highlighted the risks. The true toll that the spill exacts on the Gulf of Mexico whale shark population will not be known for some time, but the thought of dead or dying whale sharks sinking silently into the depths (dead sharks generally sink, not float) is yet more motivation to put an end to the spill and to undertake immediate and extensive research and conservation programs to assess the damage and plan a road to recovery for the whale sharks – and all the other affected wildlife – in the Gulf of Mexico.

Wednesday
Jun232010

Two videos from our recent Mexico sojourn

Below are two short videos showing some of what we got up to on a recent lightning fast trip to Mexico, footage that our AV folks spliced together from a FLIP camera I took along.  We had heard word of whale sharks gathering at one of our research sites, so I threw together a quick trip and Jeff Reid, the Aquarium's DSO, and I went down to scope it out.  It wasn't hard science this time; mostly a reconnaissance boat survey and an aerial survey, and getting to grips with the logistics for the big trips that will happen later this summer (more about those in future posts).  But at least they give a sense of what its like down there.  Next time I will try to hold the camera a bit more steady, but in the meantime - enjoy.

Sunday
Jun132010

Testing, testing...

I'm posting this video I took of a whale shark in Mexico, to test the embedding of YouTube videos in Blogger posts.

Thursday
Jun032010

The water is ALIVE!

Its easy to get discouraged about the plight of marine ecosystems and the future of all those incredible marine species that we love so much. This is especially so of late, with all the bad news about the oil spill in the northern Gulf of Mexico and the impacts that it may well have on several habitats. Consider this post, then, as your good news story for the week. I am here to tell you that there is still amazing stuff to see in the ocean. Incredible stuff. Stuff that will blow your mind. I can tell you this with supreme confidence, because for the last two days, that’s exactly what I have been seeing. As part of the research program at Georgia Aquarium, I am with colleagues in Quintana Roo, Mexico, studying whale sharks and other species that live in the azure waters of the Yucatan peninsula. Jeff Reid, who is the aquarium’s dive safety officer, is here and our main colleague in Mexico is Rafael de la Parra of Project Domino, who has been working on whale sharks and other marine species in the area for many years. This is a remarkable part of the world, with a lot of great terrestrial activities (can you say Cenotes, anyone? No? How about Mayan ruins?), exceeded only by the marine life, which is truly spectacular.

Yesterday Jeff and Raffa and I spent the day boating around the northeastern tip of the Yucatan along with videographer Jeronimo. Now, when you’re on a boat, you can only see a small strip of ocean either side of the vessel, and yet over the course of the day we saw lots of mobula (devil rays), turtles, flying fish, manta rays, spotted dolphins and whale sharks. We snorkeled alongside some of these animals and, in the case of whale sharks and mantas, took samples of their food for later analysis. They dine on the rich plankton soup of this tropical upwelling area, much of which consisted of fish eggs, which hints at other fish species – yet unseen – taking advantage of the plankton to start their next generation by spawning in the surface waters. Snorkeling next to a whale shark in the natural setting was a special thrill; I’ve been lucky enough to work with the animals in the collection at Georgia Aquarium since 2006, but this was my first encounter with them in the wild. Except for the slightly different “faces” (we do get to know our animals pretty well) and the parasitic copepods visible on the fins of the wild animal, it could have easily been the very same sharks Jeff and I have been working with in Atlanta.

Today, Jeff and Raffa and I joined Lilia (from the Mexican department of protected areas CONANP) and pilot Diego for an aerial survey of the waters around the northeastern tip of the Yucatan. In contrast to the boat, you can’t get in the water from a plane (its not advisable anyway), but you can see a whole lot more at once and cover a much greater area in a relatively shorter time. From the air, lots of sharks, cownosed rays, manta, dolphins, fish schools and whale sharks were all visible, and I am told that flamingos and manatees can be seen at other times too. The manta rays, which numbered in the hundreds, were especially impressive and included at least two species (see my post about taxonomy of mantas). The sheer number of cownosed rays, called chuchas in the local slang, was staggering (muchas chuchas, if you will). They formed huge schools that looked for all the world like the rafts of sargassum weed that accumulate on the wind-lines at the water’s surface offshore. Many of the turtles and mobula seemed to be in the mood for love; most turtles were in pairs (or a pair being followed by other hopeful males), whereas the mobula followed each other in lazy tandems, their wingtips breaking the surface with every stroke. Whale sharks were also there – lots of them – with their attendant flotilla of tourist boats and tiny orange specks of snorkelers in life-vests, doing their best (and largely failing) to keep up with the gentle giants.

When you have experiences such as those I have shared with my colleagues over the last two days, you are reminded why we do this stuff in the first place. Its not just for the papers, or the salary or the glory of new discovery (yeah, right!), its for those moments working with animals when you and a colleague become friends because you shared an experience of the oceans that most folks will never have. We should seek to share and recreate those moments with everyone we can, whether its in an aquarium or on the open ocean. I am pretty sure that if we could all do that, then public empathy for the plight of the oceans would skyrocket, and many of the threats that face them would be addressed quick smart.

Monday
May312010

Take a Levy walk on the wild side

ResearchBlogging.orgI've mentioned before that this summer I’ll be part of some whale shark field work studies in Mexico. Some of it will focus on how these amazing animals find patches of their planktonic food in the ocean. There’s a pretty good likelihood that they have an incredibly sensitive sense of smell and can detect food from miles away. They’re a bit different than toothy sharks though, because they aren’t detecting “blood in the water” as such; rather, they need to be able to distinguish patches of ocean where plankton is denser from places where its less dense. How do they do that, and what chemicals are they smelling exactly? These are among the questions we will be trying to answer.

In reading up for this work, I came across the idea of Levy Walks. This is not a walk in the sense of your evening constitutional down to the Piggly Wiggly for a 6-pack and some Slim Jims. No, it really is just the name for a certain pattern of animal movement (shown at the right), one in which animals make several short “legs” of directed motion, usually in bunches, separated by longer legs with major reorientations. Its not random motion, but neither is it all that predictable, except that the pattern exists at all scales: its fractal. In other words, if we sketched the motion of an animal on paper, and drew it to scale, it would look similar if we zoomed out to the range of kilometers instead of meters and drew the pattern again. It turns out that moving by way of Levy walks increases your chances of running into patches of food, or the trails of scent they leave behind. At that point, more directed motion takes over and the animal zig zags towards the source of that delicious scent (whereupon it becomes not too different from homing in on the Slim Jims at the Piggly Wiggly after all). Sims et al. show that Levy walks are almost ubiquitous among animals that seek mobile prey; they conclude that its a sort of biological rule for finding food that has a patchy distribution.

It’s a fascinating idea; I wonder if you could apply a deliberate Levy walk pattern if you were looking for your sunglasses, trying to find Waldo, or trying to find an empty patch of beach to put your towel on. People might look at you a bit funny, but who’d have the last laugh?

Sims, D., Southall, E., Humphries, N., Hays, G., Bradshaw, C., Pitchford, J., James, A., Ahmed, M., Brierley, A., Hindell, M., Morritt, D., Musyl, M., Righton, D., Shepard, E., Wearmouth, V., Wilson, R., Witt, M., & Metcalfe, J. (2008). Scaling laws of marine predator search behaviour Nature, 451 (7182), 1098-1102 DOI: 10.1038/nature06518

Sunday
May302010

No rest for the wicked

Returned from the Eastern Fish Health Workshop in the DC area yesterday, after our flight got canceled on Friday.  It was a fantastic meeting, for all the reasons I cited in my previous post. 

I've got one day at work today and then off to Mexico for field research with Mexican government colleagues this week (more about that later), but not for long, because teaching duties in NY on Friday and Saturday call.  While I am in NY, I'll be giving a public lecture about whale sharks at Stony Brook Southampton on the 4th at 1930hrs.  Its part of the SoMAS Spring lecture series; I'd love to see you there!

Friday
May142010

Whale sharks start to give up their secrets

ResearchBlogging.orgWhale sharks are the largest fish in the oceans; they can grow to 20m in length and weigh many tons, although 7-9m is closer to the common average these days.  Despite their tremendous size, scientists don't know that much about them.  We know that they eat plankton and that they live in the tropical oceans throughout the world and there have been quite a few papers reporting their presence in different waters, but these represent only the most basic foray into the biology of a species.  More recently, there's been a few more including one that explores genetics (Castro et al., see below) and some that have started to explore behaviour (see Brunnschweiler et al.).  Up to this point, the focus has all been external; that is, only the biology that can be observed from the outside.  That's no surprise really; its a logical place to start and there are some huge logistic challenges to working with whale sharks, as you can probably imagine.

There are 4 whale sharks in the collection at Georgia Aquarium in Atlanta and I have been lucky enough to work with these amazing animals since 2006.  Part of that work has involved veterinary examinations, which has allowed us, for the first time, to look at aspects of the internal biology of whale sharks. The first part of that work is now in print: a paper I co-authored with the aquarium's principal clinical vet, Dr. Tonya Clauss, and a colleague from National Aquarium in Baltimore, Jill Arnold (Jill is an expert in medical techniques, especially blood work), which is in the latest issue of Aquatic Biology.  Our paper is a discovery-based one (i.e. not testing a specific hypothesis) about the nature of the blood of whale sharks, both the cells and the chemistry of the blood serum.  Its open access, so you can get it at the journal web page here

In it, we show that whale sharks have blood that is fundamentally similar to that of some other sharks, specifically the bottom dwelling ones like nurse sharks and wobbegongs, but pretty different from the toothy predatory sharks like great whites.  They have very large red cells, actually white cells too, but this is something they share with the bottom dwellers, so it appears to be a feature of the group rather than a function of the size of the whale shark as such.  Whale sharks are the only pelagic members of that group, the order Orectolobiformes.  Why such large cells, then?  Our study didn't answer that question, but my best guess is that they have relatively low metabolism compared to the carcharhinids, which may need the high relative surface area of smaller red cells to improve the movement of oxygen in and out of cells.  This is the first of several hypotheses that we can only begin to pose because of these first discovery-based efforts.

I can't tell you how excited I am that we can begin to share what we've been learning at the Aquarium.  The chance to work with whale sharks is a real gift for a fish nerd like me, and the opportunity afforded by having access to them in the more controlled environment of an aquarium makes it possible to do safely and effectively research that has been prohibitively difficult with free-ranging whale sharks up to this point.  Of course, the ultimate goal is to extend that work to compliment the field research, and I look forward to telling you more about that in future posts.

Brunnschweiler, J., Baensch, H., Pierce, S., & Sims, D. (2009). Deep-diving behaviour of a whale shark during long-distance movement in the western Indian Ocean. Journal of Fish Biology, 74 (3), 706-714 DOI: 10.1111/j.1095-8649.2008.02155.x 

Castro, A., et al. (2007). Population genetic structure of Earth's largest fish, the whale shark ( )
Molecular Ecology, 16 (24), 5183-5192 DOI: 10.1111/j.1365-294X.2007.03597.x
 

Dove, A., Arnold, J., & Clauss, T. (2010). Blood cells and serum chemistry in the world’s largest fish: the whale shark Rhincodon typus Aquatic Biology, 9 (2), 177-183 DOI: 10.3354/ab00252

Thursday
Apr082010

What's a Manta do?

ResearchBlogging.org

Manta rays (Manta birostris) surely vie for the title most spectacular among the large animals in the ocean. Not only do they grow to enormous sizes, but they are placid, graceful, and generally unafraid of humans, which means we can get close to them in the water and really appreciate how incredible they are, up nice and personal. I always thought that mantas were a one-of-a-kind species - the only member of its genus - like humans, whale sharks, koala bears or killer whales. Luckily, Andrea Marshall is not like me. She and her colleagues took a closer look at the body features, colours and patterns on lots of mantas from all around the world and they concluded that there are at least two, and possibly even three, manta ray species. They’re not the first people to propose this, so technically what they have done is “resurrect” the name Manta alfredi, the Prince Alfred manta, which had been made a synonym of Manta birostris some time ago (read the paper for the full sordid taxonomic history of mantas). The differences between the two species are subtle and mostly to do with the colour of the lips, wings and shoulders, the spots on the belly and the presence or absence of a bony mass near the base of the tail, but nonetheless they probably reflect real differences between the animals and, under the current definition of “species”, they probably cannot successfully interbreed. The third potential species they call “Manta sp. cf. birostris” which is taxonomist shorthand for “as-yet undescribed manta species sort-of like M. birostris”.

If you have ever been to the Georgia Aquarium, you may have seen one or both of their mantas in the Ocean Voyager exhibit. If you look closely at these and compare them to the Marshall paper, you’ll see that one (called “Nandi”) is Manta alfredi and the other (“Tallulah”) is more like Manta sp. cf. birostris. Its slightly ironic that in light of this new paper, neither of them is the “actual” or original “manta ray”.  Of course, they are both still spectacular animals!

Who cares about all this anyway? What does it matter if there’s one or three or a dozen manta species? As it happens, it matters a great deal! Taxonomy underlies everything else in biology. What good is a population estimate, for example, if that estimate confuses two species? We would grossly overestimate both, potentially leading to overexploitation. More generally, how can we understand migration patterns, breeding grounds, diets, ecological roles or behaviour, if we are constantly confounded? These are, of course, somewhat self-centered concerns about the quality of our science or management decisions; a species count is about the most fundamental measure of nature that we have, and those sorts of diversity stats are predicated on a decent taxonomy. Consider this: how much of a ginormous “oops!” would it be if we were to protect a species in one area of ocean, only to learn that the animal in the area we didn’t protect was actually a different species?   Perhaps a more important reason it matters is for the mantas themselves and the rest of their ecosystem.  Each species has an intrinsic right to exist and a value to the ecosystem its part of. 

I just love the idea that even for familiar, charismatic mega-animals like mantas, if we look a little closer, nature shows us hidden diversity: surprising, unexpected, and exciting.

Marhsall, Andrea D., Compagno, Leonard J.V., & Bennett, Michael B. (2009). Redescription of the genus Manta with resurrection of Manta alfredi (Krefft, 1868) (Chondrichthyes; Myliobatoidei; Mobulidae) Zootaxa, 2301, 1-28

Friday
Mar192010

Whale sharks arrive early at Ningaloo Reef, Australia

I have never been to Ningaloo (great name, right?) - its WAY on the other side of Australia from where I grew up - but its a fascinating place.  Whale sharks gather there every year, and this year it looks like they turned up earlier than usual.  Whale shark aggregations are amazing events and the one at Ningaloo is one of the biggest.  Why gather? Why Ningaloo?  Why then?  How do they know where to go?  These are just some of the great mysteries of whale shark gatherings; its amazing that we know so little about the worlds largest fish.

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